An optical connector for connecting optical fibers is constituted of connecting parts which include a sleeve for an apparatus of optical communication made of ceramics such as zirconia or the like. The sleeve for optical communication is a cylindrical member having an open through-hole is configured to insert ferrules from both ends of the sleeve for optical communication so as to abut against each other inside the sleeve for optical communication. The optical fibers are respectively inserted and held in the ferrules. As the sleeve for optical communication, two types of sleeves are used, that is, one is a precision sleeve having a cylindrical shape, and the other is a split sleeve having a slit formed in a cylindrical longitudinal wall (as shown in, for example, Patent 1 to 3).
The precision sleeve and the split sleeve are respectively configured so that the inserted ferrules can be firmly held. The precision sleeve is formed so that the inner diameter is slightly larger than the outer diameter of the ferrule. Since the inner diameter of the precision sleeve is not changed by insertion of the ferrule, a highly accurate inner diameter dimension is required. On the other hand, the split sleeve is formed so that the inner diameter is slightly smaller than the outer diameter of the ferrule, and the slit is formed in an axial length direction of the split sleeve. Since the split sleeve is elastically deformed by insertion of the ferrule, the accuracy of the inner diameter dimension is not required compared with the precision sleeve.
In general, in the manufacturing of a sleeve for optical communication formed of a raw material mainly composed of zirconia, first, the raw materials containing zirconia, yttria, alumina, titania, and the like are subjected to press forming, extrusion forming, injection forming, or the like to form a cylindrical preform. Then, the cylindrical preform is fired to be hardened and, thus, to obtain a formed body. Next, treatment such as a length adjusting processing or treatment for making a length dimension in a longitudinal direction of the formed body is performed to have the length thereof equal to a predetermined length. An inner peripheral surface of the formed body is subjected to polishing processing such as honing by a diamond wheel, and such as pin grinding by diamond abrasive grains, and the like Namely, the inner diameter adjusting processing is performed so that the formed body becomes a predetermined inner diameter dimension. Next, an outer diameter adjusting processing is performed so that an outer peripheral surface of the formed body is ground with a diamond wheel using a cylindrical grinding machine or the like, so that the formed body has a predetermined outer diameter dimension. When the sleeve for optical communication is subjected to the split sleeve, a slit is formed after the length adjusting processing, the inner diameter processing, or the outer diameter processing, and the like.
In the technical field of the optical communication, regarding an optical connector, a plurality of standards are prescribed up to now. In those standards, a dimension or the like is made common for each standard to provide convenience to a user thereby. Presently, as typical optical connectors, there are the so-called SC type, FC type, MU type, and LC type optical connectors. In the outer diameter dimension and the like of the SC type optical connector, the outer diameter dimension and the like of the SC type optical connector are specified in the standard of IEC 61754-4, TIA/EIA-604-3A, and JIS C 5973. The outer diameter dimension and the like of the FC type optical connector are specified in IEC 61754-13, TIA/EIA-604-4A, and JIS C 5970. Next, the outer diameter dimension or the like of the MU type optical connector is specified in IEC 61754-6, TIA/EIA-604-17, and JIS C 5983. Further, the outer diameter dimension or the like of the LC type optical connector is specified in IEC 61754-20 and TIA/EIA-604-10A.
The inner diameters of the SC type optical connector and the FC type optical connector, and the outer diameter of a ferrule which holds the connectors thereof are respectively about 2.5 mm And the inner diameters of the MU type optical connector and of the LC type optical connector are respectively about 1.25 mm. Specifically, it is provided that the outer diameter dimensions of the SC type ferrule and the FC type ferrule which are classified into grade 1 in IEC 61754-4, IEC 61754-13, TIA/EIA-604-3A and TIA/EIA-604-4A and grade B in JIS C 5973 and 5970 are respectively specified as 2.499±0.0005 mm. Moreover, the outer diameter dimensions of the MU type ferrule and the LC type ferrule classified into grade 1 in IEC 61754-6, IEC 61754-20, TIA/EIA-604-17 and TIA/EIA-604-10A and grades B and C in JIS C 5983 are respectively specified as 1.249±0.0005 mm. In each optical connector, the outer diameter dimension of a housing is also specified by the IEC standard, the JIS standard, or the TIA/EIA standard.